In 1506, Leonardo was summoned back to Milan by Charles d'Amboise, French governor of Lombardy. Now an international celebrity, the artist was in high demand; and after his move, the Florentine government often sent letters to d'Amboise, petitioning the French to let Leonardo return to Florence. They wanted him to complete the Battle of Anghiari, which they had already paid for. As always, however, Leonardo gave preference to his own wishes, and this meant staying in Milan, a city where he had always felt comfortable.
The Confraternity of the Immaculate Conception, which had originally commissioned the Virgin of the Rocks, had for a long time been involved in legal battles with the brothers de' Predis, who had painted the side panels. Now, Leonardo had to return to the painting and supervise a new version. He may have done some of the actual work himself, as well; some critics think they see his hand in the angel's face. Certainly, his changing style is seen in the more aged and large-bodied Mary.
In general, Leonardo's fortunes were on the rise. He soon became painter and engineer to Louis XII, King of France. In 1507, while traveling in the surrounding countryside, Leonardo met the young Francesco Melzi. The boy was 15 years old. Melzi, a thick-haired boy with almond-shaped eyes, became one of Leonardo's most beloved "pupils," along with Salai.
Later that year, in 1507, Leonardo had to return to Florence: when his father had died without a will, in 1504, his legitimate sons had claimed all of the inheritance; now, Leonardo's uncle Francesco had died, and had left a large amount to Leonardo. However, Leonardo's brothers again tried to cut Leonardo out of his share, and this time Leonardo took them to court. He even had Louis XII write to the court officials in Florence to speed up the legal proceedings. The dealings lasted nearly six months.
Both while still in Florence and then while back in Milan, Leonardo increased work on his anatomical studies. He sketched practically every organ in the body, each one from different angles–an unusually modern technique for the sixteenth century. Leonardo also seriously engaged himself in studies of hydraulics.
Leonardo's interest in anatomy probably led to an interest in illustrating the myth of Leda and the Swan. According to the myth, Zeus assumed the form of a swan in order to seduce and impregnate the beautiful Leda. Such an intense scene of bodily struggle between beast and human no doubt fired Leonardo's anatomically oriented imagination.
By the time Leonardo met Melzi, Salai was about thirty years old. He may have been jealous of this new "beautiful boy." Whatever the nature of the relationship between Melzi and Leonardo, it is clear that they became intimate rapidly. While Leonardo was in Florence awaiting the outcome of his lawsuit, he wrote several letters to Melzi, and asking that his letters be answered. They are written in a casual tone. On the other hand, while Salai produced little art while living with Leonardo, Melzi was much more of a serious student, and we have several drawings and paintings from Melzi's later years.
Leonardo was by this time growing old, and his output lessened. He undertook fewer large paintings, instead focusing on his primary interests, which at the time seem to have been more scientific than artistic: with increasingly grandiose patronage–in this case the King of France–Leonardo seems to have had increasing freedom to pursue his own goals. However, it is also possible that Leonardo spent the greater part of these years working on the Mona Lisa, as scholars cannot be certain that the painting was yet complete.